Channel Sinuosity Effects on Inland Transport in the Riverine Region

of Ilaje, Nigeria

BABATOPE SUNDAY OLISA1, MOBOLAJI STEPHEN STEPHENS2, IKPECHUKWU. NJOKU3,

CHIAMAKA LOVELYN OLISA4

1,2,3 Department of Logistics and Transport Technology,

Federal University of Technology, Akure, NIGERIA

4 Department of Urban and Regional Planning,

Federal University of Technology, Akure, NIGERIA

Abstract: Transportation is an essential tool for regional social and economic growth, as well as national

development. Transport has a vital social and environmental impact that cannot be overlooked. The character of

naturally functioning rivers varies greatly and does not remain constant since it is mainly determined by several

of physical factors and processes, among which is river sinuosity. Understanding how the inland waterways

change with time and the effect or consequences of these changes on the lifestyle and economic activities of the

inhabitants becomes very important. This study focused on revealing the changes that had occurred in the

planforms of Igbokoda-Idiogba/Ayetoro waterways in Ilaje, Ondo state; its effects on inland transport taking

cognisance of sinuosity index. It assessed morphological changes of navigable rivers in the study area from 1972-

2022; the effects of river sinuosity on inland transport in the study area were considered. The study deployed

geospatial techniques to assess the decadal changes of changing patterns of the channel’s sinuosity taking

cognizance of the sinuosity index and formula. However, the study shows the capabilities of geospatial techniques

in monitoring river morphology. The study revealed significant changes in the channel’s sinuosity and

consequential effects of the changes. Sustainable transport measures for safety and efficiency were

recommended.

Key-Words: - Inland, Waterway, Sinuosity, River, Curvature, Transport, Channel

Received: July 7, 2023. Revised: May 11, 2024. Accepted: June 14, 2024. Published: July 24, 2024.

1 Introduction

Rivers that function naturally have a highly variable

character that changes over time due to a multitude

of physical factors and processes, including substrate

caliber, bank line shifting, valley gradient, sinuosity,

and depth variability caused by sedimentation and

silting. Nonetheless, effective transportation systems

offer social and economic advantages and

opportunities that have a beneficial knock-on effect,

improving market accessibility, creating jobs, and

drawing in more capital. However, there can be social

and/or economic consequences as well as a

significant likelihood of a decline in quality of life

when transportation networks are deficient in terms

of capacity or reliability [1]. One of the challenges

that Nigerians face when using waterways is health

and safety. Mistakes at river curvatures (bends),

vessel overcrowding and/or listing resulting in

capsize at bends, poor watercraft, and sunken wrecks

above and below the surface are among the causes of

many waterway accidents, riverbed silting, and the

disappearance of navigable channels in littoral states.

Aside from natural causes, river sinuosity can be

altered by human activity. However, the intricate

structure of rivers, as well as increased interest in

quantitative analysis of this complex structure, has

prompted this study, and it is an essential area in river

science that this study focuses on.

River plan change is seen as the resultant effect of

change in depth, width, discharge, and the pattern of

sinuosity of a river (river curvature) among which are

Oluwa River, its tributaries, and distributaries

threaten safe navigation for rural communities of the

Ilaje area. Inland navigation becomes threatened

when there is frequent shifting in river bank lines and

changes in river depth due to accretion or

sedimentation of material in riverbeds [2]. River

channel changes such as bank erosion, downcutting,

and bank accretion are natural processes for an

alluvial river [3], all these natural processes have

effects on inland waterways especially their

navigability, environment and socio-economic

benefits to locals in their catchment areas. The

existence of the waterways has been an important

factor in the development of several riverine

communities in Nigeria; for instance, River Niger

International Journal of Environmental Engineering and Development

DOI: 10.37394/232033.2024.2.19

Babatope Sunday Olisa,

Mobolaji Stephen Stephens, Ikpechukwu.

Njoku, Chiamaka Lovelyn Olisa

E-ISSN: 2945-1159

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had been an important artery connecting transport

activities from the north to western geopolitical

regions to south and eastern geopolitical regions; and

waterways have served first as paths of exploration

and new settlement and later as avenues of commerce

and trade in Nigeria [4]. It becomes crucial to

comprehend how inland rivers change over time and

the effects these changes have on the way of life and

economic activity of the locals. This study

emphasizes the effects of channel sinuosity on inland

transit as one of the behavioral patterns of navigable

rivers in the riverine region of the Ilaje local

government area, Ondo state.

Water transport projects must be planned,

designed, and carried out with an understanding of

how river morphology changes over time. In order to

advance understanding and create policies that will

promote sustainable economic growth in the

catchment areas, the study explored the effects of

river sinuosity on inland transportation and

socioeconomic activities in the riverine area of Ondo

state. The results of this research will provide new

information that might be used as a platform for

planning and appropriate management of the Oluwa

River and other rivers in the study area, as well as

guidance to decision makers on inland waterways

planning projects. In developing countries, rural

transportation is frequently neglected and not

integrated into transportation planning [5].

2 Study Area

The study area is located within the riverine area of

Ilaje Local government area of Ondo State, Nigeria.

Ondo State lies specifically on Latitude 7010’N and

Longitude 5005’E. It is located in the South western

geopolitical zone of Nigeria and bounded in the

North by Ekiti and Kogi States, in the East by Edo

State, in the west by Osun and Ogun states and in the

south by the Atlantic Ocean (see Fig. 1). Ondo State

is located entirely within the tropics. It has a

population of about 3,441,024 [6].

SCALE: 1 : 40.5m

2° E 4° E 6° E 8° E 10° E 12° E

12° N

10° N

8° N

6°N

4° N

12° N

10° N

8° N

6°N

4° N

2° E 4° E 6° E 8° E 10° E 12° E

SOKOTO

KEBBI

BAUCHI

KANO

JIGAWA

ZAMFARA

KATSINA

KADUNA

NIGER

BENUE

PLATEAU

NASSARAWA

YOBE

ONDO

GOMBE

EKITI

ADAMAWA

BORNO

F.C.T

OSUN

KWARA

KOGI

TARABA

OGUN

LAGOS EDO

BAYELSA RIVERS

ANAMBRA

IMO CROSS RIVER

ABIA

ENUGU

DELTA

EBONYI

AKWA IBOM

OYO

NATIONAL BOUNDARY

STATE GOVERNMENT BOUNDARY

FEDERAL CAPITAL TERRITORY

RIVER

ONDO STATE

F.C.T

L E G E N D

Fig. 1: Ondo State Map its National Setting

Source: [7]

Fig. 2: Oluwa River Network and other water bodies

in Ilaje Local Government Area

Source: Adapted by the Author from [8]

In this study, emphasis is given to a section of river

reaches of the waterway channel of River Oluwa in

Ilaje Local Government Area (LGA) being part of the

creeks that crisscrossed the main mangrove

vegetation of the landscape in the riverine area. The

water body flows through inner communities from

the west border to the eastern border of Ilaje LGA

dissecting the local government area into two

geographical parts as shown in Fig. 2. River Oluwa

was selected for the study due to its significant

geographical location, network and its connections to

several communities. At its middle course, a

distributary ‘Igbokoda-Idiogba/Ayetoro waterway

channel’ connects its network down to Ayetoro

where it empties its water into the Atlantic Ocean.

Igbokoda-Ugbonla-Idiogba/Ayetoro waterway is

found to be the busiest inland waterway corridor in

the area hence, its selection as the study area. This

International Journal of Environmental Engineering and Development

DOI: 10.37394/232033.2024.2.19

Babatope Sunday Olisa,

Mobolaji Stephen Stephens, Ikpechukwu.

Njoku, Chiamaka Lovelyn Olisa

E-ISSN: 2945-1159

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river corridor serves as a major means of

transportation for both freight and passengers,

providing access some isolated locations within the

study area. As stated by Parikesit in his studies

between 2003 and 2005, the role of river or inland

water transport has become very prevalent and

important, particularly when it is the only means of

accessibility by passengers and freight movement to

remote areas [9].

3 Related Reviews

Determining the effects of river shape on human

socioeconomic status, quality of life, and

environmental quality is crucial, as evidenced by the

growing interest in sustainable inland waterway

transport systems and growth [10]. In its January

plenary meeting in 2022, the European Economic and

Social Committee (EESC) endorsed smart shipping

and multimodal transportation, emphasizing the need

for inland waterway transportation to be maintained

and developed [11]. Furthermore, as compared to

other modes, inland waterway transport (IWT) is

acknowledged as being energy-efficient, having a big

freight capacity, and a lower level of greenhouse gas

emissions. Consequently, IWT supports the 2030

Agenda's Sustainable Development Goals (SDGs)

for Sustainable Transport to be achieved. Szymanski

opined that nonetheless, transportation sustainability

assessments must consider environmental, social,

and economic factors [12].

It is clear that scholars researched literature and

investigated facts about river morphology,

socioeconomic roles, cultural effects, and

environmental implications. In addition, various

studies on river morphology have been conducted,

including sinuosity, planform change, river shifting,

banklines shifting, the use of geographic information

systems and methodologies, spatiotemporal studies

of river plan change using time series analysis, and

so on. Among these literatures are: a review and

outlook of river morphology expression by [13]. The

study asserted that river is a crucial component of the

global water and energy cycle [14] which

morphology has been changing frequently over the

last few decades due to human activities

(anthropogenic factors) and weather conditions

(climate change) [15]. The study focused on

summarizing existing data and methods of river

morphological expression in various disciplines;

analyzing the main challenges and limitations faced

by various river morphological expression models

and methods. Thereafter, the study proposed future

directions of the river for a detailed understanding of

river morphology in the study area.

Ahmad conducted research on the Rapti River

basin in India utilizing remote sensing and GIS

techniques. His findings revealed that rivers with

considerable seasonal variations in discharge and

sediment loads underwent major morphological

alterations [16]. The investigation also revealed

significant losses as a result of the river's channel

shifting as cultivated and expensive agricultural land

eroded. Sediment deposition and erosion in and along

the river channel had a significant impact on the

river's cross-section, gradient, sediment transport

rate, and discharge; however, understanding changes

in river morphology is critical for engineering project

planning, design, and execution. His research found

that the river's behavior generated major changes in

the river's bank lines, sinuosity, and depth

fluctuation.

Dewan used geospatial tools to quantify channel

parameters in two key reaches of Bangladesh's

Ganges system during a 38-year period [17]. They

also considered the Ganges and Padma rivers' bank

line shifts, their nature and extent, and assessed the

amount and location of erosion and deposition in the

river channel. The analysis found that the river

contracted and expanded, as well as changed its plan

form. Furthermore, an examination of left and right

bank movement revealed that each bank has distinct

stretches with high and low movement [17]. Schwenk

studied changes in the plan form of a river with vivid

meandering features at high spatiotemporal

resolution [18]. The study used Landsat imagery, and

the findings provided a foundation for determining

controlling factors influencing local planform

changes and contextualizing them within a broader

context. The study used the RivMAP toolkit, which

provides easy, easily customisable, and parallelizable

Matlab scripts for evaluating meandering river masks

produced from satellite images and aerial

photography. Estimates of uncertainty associated

with categorizing and compositing Landsat data were

used to generate useful annual morphodynamic

information on big rivers [18]. Yu et.al established in

their study a weighted usable area curve to identify

inflection points and maximum values in determining

the ecological flow under different sinuosities in

Nansha River, Beijing. The study clarified the

relationship between sinuosity and ecological flow

[19]. This study reviews the related studies to unveil

fundamental understanding about the dynamic of

sinuosity and its associated morphological influence

on riverways.

International Journal of Environmental Engineering and Development

DOI: 10.37394/232033.2024.2.19

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Mobolaji Stephen Stephens, Ikpechukwu.

Njoku, Chiamaka Lovelyn Olisa

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4 Methods

Morphological investigation was carried out on a

section of the river reaches of River Oluwa from

Igbokoda town through Legha, Mahin/Ugbonla to

Idiogba/Ayetoro and Eruna-Ero waterways. This

river segment was selected being the busiest inland

waterway route serving as a major means of

connectivity and accessibility by passengers and

freight movement for many remote communities to

Igbokoda (the commercial hub) in the local

government area. The river segment was demarcated

into reaches and sub-reaches for detailed

morphological analysis.

The study adopted geospatial techniques to

conduct spatiotemporal analysis of the river plan

changes. Temporal scope of the study spanned

between 1972 and 2022. The study explored satellite

data and GIS Techniques for this purpose. Map data

for river planforms between year 1972 and 2022 were

collated, assessed and analysed using ArcGIS and

Automated Computer Aided Techniques. Satellite

data captured and used for the study include Landsat

MSS TM 1972, Landsat ETM+ 1984, 2002, 2012,

and 2022 Imageries. The satellite data were

compared in the post-classification comparison for

change detection. Unsupervised Image classification

was deployed which involved ISO cluster

unsupervised classification with optional minimum

class size after which a reclassify was done to identify

variations in the channel line over the years. Changes

in waterbodies and river bank line class are primarily

emphasised in the study. The meandering sections of

the waterway were taken into consideration. This

approach was considered suitable and appropriate to

identify directions of meander movement and erosion

using the average meander length and meandering

centroids.

Fig. 3: River plan form of the study area

Source: Author, 2023

The sinuosity index was deployed for the study to

identify the extent of curvatures and determine the

sinuous state of the reaches under study. This is in

agreement with [20], the sinuosity index can be

utilised in defining the detailed types of the river

channel such as the straight, sinuous, meandering,

and extremely meandering channels [20] Sinuosity

Index formula is depicted in Fig. 4 as described by

Leopold, Wolman, & Miller (1964) and as follows:

SI =Thalweg length

Valley length …………….. (1)

Fig. 4: Typical Shape of Channel Sinuosity between

the end points of the curve.

Source: [21]

Sinuosity is a measure of how much a river (or

other linear feature) deviates from being straight. It

describes the curvature state of a river channel. As

shown in table 1, a truly straight river has a sinuosity

of 1; as the number of meanders increases, sinuosity

approaches [22]. The Ratio of the sinuosity index

indicates how the curvature of the river channel can

be by measuring the length of the reach (a section) of

river channel and dividing by the straight-line

distance along the valley [23]. See Table 1.

Table 1: Classification of Sinuosity Index

Type

Sinuosity

Straight

Sinuous

Meandering

SR<1.1

SR =1.1 to 1.5

SR>1.5

Straight

< 1.1

Sinuous

1.1 – 1.5

Meandering

> 1.5

Source: [23]

Fig. 5: Definition of channel morphology based on feature

parameters

Source: [24], [13]

International Journal of Environmental Engineering and Development

DOI: 10.37394/232033.2024.2.19

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Mobolaji Stephen Stephens, Ikpechukwu.

Njoku, Chiamaka Lovelyn Olisa

E-ISSN: 2945-1159

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Besides, sinuosity is a measure of how much a

river (or other linear feature) deviates from being

straight. According to [24], the sinuosity index is

measured as channel length along the thalweg (a line

drawn through the deepest points of successive cross-

sections along the length of the channel, divided by

valley length. It describes the curvature state of a

river channel regarding its navigability. It is expected

that this study will give information on the areas that

are safe for navigation or susceptible to accidents

such as collision, grounding and ramming into

submerged objects by watercraft or vessel.

5 Results and Discussion

A morphological survey was conducted on selected

reaches (sections) of the Oluwa River, which is the

distributary of River Oluwa (Ugbonla-

Ayetoro/Idiogba river channel). The results obtained

from the investigation represent a fractional

condition of the river and its influence on inland

transportation in Ilaje Local government area. The

study addressed change analysis of river plan form

(channel patterns), and river banklines (shorelines)

with emphasis on river sinuosity; its effects on inland

transport were addressed in the study area.

5.1 Changing Pattern of Sinuosity Index (SI)

The section of the river channel from Igbokoda-

Ayetoro/Idiogba was divided into four (4) Reaches

A, B, C and D, for detailed analysis; while

subdivisions into sub-reaches were done given a total

number of forty-six (46) sub-reaches. Findings

revealed that the channel patterns exhibit

configurations such as straight, sinuous, meandering

and braiding. These configurations are best described

by sinuosity which is the ratio of channel length to

valley length or the ratio of valley slope or channel

gradient as measured over the same length of valley.

Table 2 shows that there were significant changes

in the sinuous of the river sections from Igbokoda to

Ayetoro/Idiogba over the period of 50 years. The

waterway channel exhibited some erosion and

deposition processes causing such significant

changes in its shapes and curves. The intensity of

these curves was determined using the channel

sinuosity index. Channel sinuosity is calculated by

dividing the length of the stream channel by the

valley length (straight line distance) between the

endpoints of the selected channel reach. See Fig.4.

Table 2: Sinuosity values of different Reaches of the waterway from Igbokoda to Ayetoro between 1972 and 2022

River

Channel

1972

2022

1972

INDEX

S = Lc/Lv

2022

INDEX

S = Lc/Lv

Index

variations

Channel

length

variation

Valley

length

variation

SINUOSIT

Channel

Length

Valley

Length

Channel

Length

Valley

Length

REACH

SRH 1-4

4569.78

2921

4627.58

2921

1.5645

1.5842

0.0198

57.8

SRH 6-10

5007.63

2425.3

5100.88

2438

2.0647

2.0922

0.0275

93.25

12.7

SRH 9-12

3936.9

1498.3

4088.84

1498.3

2.6276

2.7290

0.1014

151.94

SRH 11-13

2943.51

1622.4

3087.67

1622.4

1.8143

1.9031

0.0889

144.16

SRH 14-15

1361.18

1166.6

1362.99

1166.6

1.1668

1.1683

0.0016

1.81

REACH

SRH 1-4

4418.62

2714.4

4397.32

2714.4

1.6278

1.6200

-0.0078

-21.3

SRH 5-8

4103.18

3838.2

4110.95

3838.2

1.0690

1.0711

0.0020

7.77

REACH

SRH 1-3

3100.14

2816.2

3082.47

2816.2

1.1008

1.0945

-0.0063

-17.67

SRH 4-8

5108.12

4818.1

5072.33

4818.1

1.0602

1.0528

-0.0074

-35.79

REACH

SRH 1-4

4476.78

4018.5

4524.72

4018.5

1.1140

1.1260

0.0120

47.94

SRH 5-9

4363.7

4037.7

4345.41

4071.96

1.0807

1.0672

-0.0136

-18.29

34.26

SRH 10-11

2035.41

2166.1

2048.1

2199.88

0.9397

0.9310

-0.0087

12.69

33.78

SRH 12-14

3152.84

3004.7

3104.64

3004.7

1.0493

1.0333

-0.0160

-48.2

Average Channel length

REACH A= 448.96m

REACH B= -13.53m

REACH C=-53.46m

REACH D= -5.86m

Total Channel Length

1972 Channel Length= 48,577.79m (48.58km)

2022 Channel Length = 48,953.9m (48.95km)

Channel Extension = 376.11m (0.376km)

S = Sinuosity Index; Lc= Length of channel; Lv = Valley Length

Source: Author, 2024

International Journal of Environmental Engineering and Development

DOI: 10.37394/232033.2024.2.19

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Mobolaji Stephen Stephens, Ikpechukwu.

Njoku, Chiamaka Lovelyn Olisa

E-ISSN: 2945-1159

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Volume 2, 2024

The sinuosity index is mathematically expressed as:

SI =Lc

that is: SI =Channel length

Valley length where, SI is Sinuosity

Index; Lc is channel length and Lv is the Valley

length

As observed in the study, the variations in the

values of sinuosity indicate erodibility and deposition

of sediments occurring in the river bed with resultant

effects on depth changeability and channel length

extension. This event of action usually results in

uncertainties in the river depth and unpredictability

in inland navigations. The propensity for vessels or

watercraft in transit to run aground is high with

rapidly changing river depth, width, shapes,

structures and other uncertainties. Sinuosity values

recorded in 1972 and 2022 revealed a significant

change in the shape and patterns of the Igbokoda-

Ayetoro/Idiogba waterway. Table 2 and Fig.6

indicated that the sinuosity values for sub-reaches 1-

4, Sub-reaches 6-10, Sub-reaches 9-12 and Sub-

reaches 11-13 between 1972 and 2022 had sinuosity

index values greater than 1.5.

According to [13], sinuosity greater than 1.5 is

highly meandering. This is the section of river

reaches that traverse Igbokoda through Kajola to

Ebute Ipare. Sub-reaches 1-4 had a sinuosity index of

1.5842, SRH 6-10 recorded 2.0922 indices, 2.7290

was estimated for SRH 9-12 and SRH 11-13 had a

1.9031 sinuosity index value. All of these sub-

reaches are found in Reach A and can be referred to

as highly meandering channel. This is in agreement

with [25] asserting that highly meandering channels

have a sinuosity index value exceeding 1.50 (see

Fig.5). The ending section of Reach A is constituted

by SRH14 and SRH15 which connects Ebute-Ipare

remained relatively sinuous with 1.166 and 1.168

index values. However, the consequential effects of

this change included channel extension and channel

stretching.

Fig. 6: Planform view of Meandering section of the river

reach A

Source: Author, 2024

Findings revealed that the river channel extended

in length. As shown in Table 2, in 1972, the river

channel length was 48,577.79m (48.58km) long; but

in the year 2022, the channel had increased in length

to 48,953.9m (48.95km). The river sections, which

include Reach A, B, C, and D, extended (stretched)

by 448.96 metres over a 50-year period (1972-2022);

however, this is owing to changes in the course of the

river channel caused by river flow and erosion. The

meandering part of the Igbokoda-Ayetoro/Idiogba

canal is distinguished by shifting positions, as it

exhibits a snakelike shape with meandering rivers

flowing through its valley, eroding sideways and

slightly downstream. Table 2 shows the changes in

valley and channel lengths based on the selected

reaches.

Investigation of river velocity at river bends

indicated that the river flow moved sideways because

the maximum velocity of the stream shifted to the

outside of the bend, causing erosion of the outer bank.

Simultaneously, the lower stream on the inner bend

of the meander causes silt deposition. Thus, by

eroding its outer bank and depositing material along

its inner bank, the river moves sideways without

affecting its channel size. However, the channel

length (distance) varies as the stream flows faster

through its protrusion force around these curves and

causes the channel to increase in length. (see Fig.7).

This was supported by [26] Writer (2020) that as

meanders grow by extension, the channel length

increases.

International Journal of Environmental Engineering and Development

DOI: 10.37394/232033.2024.2.19

Babatope Sunday Olisa,

Mobolaji Stephen Stephens, Ikpechukwu.

Njoku, Chiamaka Lovelyn Olisa

E-ISSN: 2945-1159

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Fig. 7: Action of river flow at river’s inner and outer

bends

Source: Author, 2024

As a general rule, a river’s current flows fastest

where the channel is deepest and there are fewest

obstructions. When a riverbed contains a meander,

the water moves in what is known as a helicoidal

flow. In a helicoidal flow the main current

corkscrews from one side of the river to the other,

creating more erosion and carving out a deeper

channel on the outside of the meander. River reach B

was sectionalized into 4 sub-reaches 1, 2, 3 and 4. It

traverses Negboro, Kurawe to Ibila on meandering

lanes with a sinuosity index value of 1.62. Other

reaches studied include Reach C and Reach D which

showed a clear straight index value of less than 1.1.

This observation is traceable to the dredging and

channelization project carried out in 2011 by

OSOPADEC and NDDC on the section of the river

along the Ugbonla to Ayetoro/Idiogba waterway

Conclusively, it is noteworthy that between 1972

and 2022, the Igbokoda-Ayetoro-Idiogba river

channel exhibited meander-sinuous and straight

configurations within sinuosity parameters of less

than 1.1 and greater than 1.5 index values. From 1972

to 2022, the sinuosity of the riverway had a

significant change and extension in channel length

with a tendency to continue as the year progressed

teething troubles to inland navigation and transport

especially at the meandering sections specifically

Reach A (see Fig.6). For instance, in 1972, Reach D

sub-reaches 1-4 was on the straight index value of

1.05 (below 1.1); but as at 2022, its morphological

status changed to sinuous with a 1.13 increase in the

sinuosity index value (above 1.1 Straight threshold

index value). At Reach A, sinuosity parameter is

relatively high compared to Reaches B, C and D.

Besides, between 1972 and 2022, the sinuosity

parameters seemed to be negative, very low and

having a proportional decrease in sinuosity as shown

in Table 2. This subtle drop in the sinuosity index of

these reaches is an indication of the impact of inland

waterway dredging and channelization projects done

in the river channel in 2011.

5.2 Changing Pattern of Sinuosity and Inland

Transport in the Study Area

5.2.1 Increased Travel Distance and Operating

cost:

Findings revealed that the length of the river channel

extended by a distance of 448.98metres. As of 1972,

the travel distance on the waterway from Igbokoda to

Ayetoro/Idiogba region was 48,577.79m (48.58km);

in 2022, the travel distance is estimated as 48,953.9m

(48.95km). Fig.8 depicts both negative and positive

fluctuations in values of the channel lengths of 1972

and 2022 river planforms. The positive values

connote channel length extension, while the negative

values show channel length reduction. The positive

variations are apparent in Reach A (SRH 1-4, SRH 6-

10, SRH 9-12 and SRH 11-13), Reach D (SRH 1-4

and SRH 10-11). The analysis showed that the river

channel extended in length by 448.96m (0.449km)

over the period of 50 years. However, this has direct

negative effects on travel distance and operating cost

of transport particularly fuel energy consumed. A

Theory states that ‘the longer the travel distance, the

fuel consumption and the higher the operating cost to

travel’ [27]. The standard error reflected that the

values are of a high percentage of accuracy with no-

skewed error bar. It is note taking that the

determinants of vessel fuel consumption can be

directly related to the type of vehicle engine, vehicle

travel distance, and vehicle load on reductions of

energy used. The effects of potential future changes

in vessel travel distance while other factors remain

constant are significant in operating cost on fuel. This

is in agreement with Sivak who asserted that the

amount of fuel consumed is directly proportional to

vehicle distance travelled (holding everything else

constant) [27] (Sivak, 2013). Thus, any proportional

increase in the vessel’s travel distance (e.g., by an

increase in the length of the channel) would translate

into same proportional increase in fuel used for

transportation (operating cost).

International Journal of Environmental Engineering and Development

DOI: 10.37394/232033.2024.2.19

Babatope Sunday Olisa,

Mobolaji Stephen Stephens, Ikpechukwu.

Njoku, Chiamaka Lovelyn Olisa

E-ISSN: 2945-1159

218

Volume 2, 2024

Fig. 8: Standard Error of the Channel Length variations of 1972 and 2022 river planforms

Source: Authors, 2024

5.2.2 Increase Cases of Grounding or

Ramming

The navigability of a riverway usually becomes more

uncertain particularly on the meandering sections due

to the degree of depositions on its convex banks and

erosion corkscrewing the concave banks. Because of

the structure of the riverbeds, the water continues to

exaggerate the differences in depths between the

inside and outside of the meander. This makes these

parts of the channel unsafe for navigation;

watercrafts become susceptible to accidents such as

collision, grounding and ramming into submerged

objects. Fig.9 shows potential accident-prone spots

on the meandering lanes in the waterway. A boat

accident that occurred at Osumaga, Ilaje in 2002 was

attributed to collision and ramming against a larger

wooden watercraft. The accident claimed the lives of

12 passengers; though, 45 adults and 35 children

were rescued. According to Wilzbach and Cummins,

sinuosity index is measured as channel length along

the thalweg (a line drawn through the deepest points

of successive cross-sections along the length of the

channel, divided by valley length [25]. The safest

path for vessel passage is the Thalweg line in the river

channel as shown in Fig.9. Most of the boat operators

in the study area rely on their pre-knowledge in

identifying safer paths in red dotted line (Thalweg

line positions) on riverways; this is not safe enough

for vessel navigations as the channel bed levels and

Thalweg line positions at river bends exhibit

continuous change over time. Kastrisios and Ware

asserted that the need for constant updates of

bathymetric data and production of nautical charts

becomes more prominent in contemporary maritime

navigation with the increasing sizes of watercrafts

that operate in tighter or narrower spaces or waterway

channels [28].

Fig. 9. Cross Section Formations at River Curvatures

Source: [29]; [30] adapted by Author, 2024

As shown in Fig.9, cross-sections A-A and C-C

revealed actions of bottom and surface currents on

erosion and deposition of sediments in the river

reaches, while cross-section B-B shows a passage

free for safe navigation. Identifying recurrent

changes in morphology of river is necessary in the

production of nautical charts for save ferry/vessel

navigation.

5.2.3 Increased Difficulty in Manoeuvring

Findings revealed that several curvatures are found

in-between reach A (Igbokoda -Perawe waterway

corridor). Reach A had an increased river curvature

with a sinuosity index above 1.5; this part of the river

is highly meandering. The greater the degree of

RH A

SRH

1-4

RH A

SRH

6-10

RH A

SRH

9-12

RH A

SRH

11-13

RH A

SRH

14-15

RH B

SRH

1-4

RH B

SRH

5-8

RH C

SRH

1-3

RH C

SRH

4-8

RH D

SRH

1-4

RH D

SRH

5-9

RH D

SRH

10-11

RH D

SRH

12-14

Σειρά1 57,8 93,25 151,94 144,16 1,81 -21,3 7,77 -17,67 -35,79 47,94 -18,29 12,69 -48,2

57,8

93,25

151,94 144,16

1,81

-21,3

7,77

-17,67 -35,79

47,94

-18,29

12,69

-48,2

-100

-50

100

150

200

CHANNEL VARIATION

RIVER REACHES

International Journal of Environmental Engineering and Development

DOI: 10.37394/232033.2024.2.19

Babatope Sunday Olisa,

Mobolaji Stephen Stephens, Ikpechukwu.

Njoku, Chiamaka Lovelyn Olisa

E-ISSN: 2945-1159

219

Volume 2, 2024

sinuosity index of the meandering waterway, the

wider is the angle of deflection and the more

vulnerable vessels are to collision against the river

banks or with another vessel. Minimum speed is

expected at river curvatures for vessels in transit to

manoeuvre on their lanes. Boats operator are

encouraged to reduce speed at bends to avoid

collisions either against the river banks or other

vessels on the water. The observed bends (river

curvatures) as indicated in Fig. 10 require more

precise manoeuvring, as there is less room for error

due to the narrowness of the channel. The average

channel width of the Igbokoda-Ayetoro waterway is

been estimated as 50metres for two-way

manoeuvring lanes. This can be challenging for

larger vessels or those with limited manoeuvrability

particularly when the river curvature is narrow. Fig.

10 shows the typical manoeuvrability positions of

watercraft in opposite directions at the curvature of

the waterway channel. It indicates that the difficult

situation of narrow width is more pronounced at

channel bends or curvatures as vessels tend to sway

sidewards (at swept path zone) on the manoeuvring

lane before adjusting back on the straight.

Fig. 10: Typical manoeuvrability positions of watercrafts

in opposite directions at river curvature (bends) - (swept

path zone); Source: Adapted from [30].

5.2.4 Slower Speeds and Increased Travel Time

Boat speed can be determined by various factors,

including the river's width, depth, curvatures, current,

and the presence of obstacles such as rocks, sandbars,

or other boats. Travel time between Igbokoda and

Ayetoro increased due to the channel extension and

increase in the angle of deflection in some reaches of

the waterway channel. Narrower and bend sections of

the reaches require vessels (watercraft) in transit to

slow down, as there is less sight distance (visibility)

and less room for two vessels (watercraft) on the two-

way manoeuvring lanes to manoeuvre; hence high

risk of collisions. This usually leads to increased

travel times and reduced efficiency. Taking

cognizance of speed and minimum sight distance,

Benetou and Tate asserted that the operating speeds

are considerably lower at locations where the

minimum sight distances are below 250 feet (76.2m)

than at locations where the lowest sight distances are

greater than 500 feet (152.4m). [30], [31]. The radius

of the curve and the angle of deflection are directly

related to visibility or sight distance and the speed of

vehicle on curvatures. Hence, the minimum

permissible boat speed on a meandering riverway

needs to be ensured, considered and adhered to by

boaters because a slower speed will give the boat

driver enough time to sight and avoid unwanted

collisions against opposite objects or obstacles.

Minimum permissible boat speed refers to the lowest

speed at which a boat can safely navigate a river that

has bends or curves. It is set to ensure that watercraft

can safely navigate the river or at its bends without

causing damage to the environment or posing a risk

to other boaters.

Fig. 11: Illustration of the Angle of Deflection and vessel’s

manoeuvrability at river curvature

Source: Author, 2024

6 Conclusion

The study revealed banklines shifting, channel

elongations, an increase in deflection angles at river

curvatures/bends and the potential depth variability

in the river beds at bends. All of these occurrences

had resultant effects on inland transportation and its

users in the form of increased travel time, distance

and difficulty in watercraft manoeuvres in the river

reaches. The results of the sinuosity index showed the

effects of aggradation at inner bends and degradation

at outer bends in the reaches during different flow

conditions of the river. These caused variations in the

channel patterns as there are observed differences in

sinuosity indexes. Reach A (SRH 1-13) reveals the

more unsafe conditions of accidents/incidents such as

grounding, ramming, collision and likely flood

hazards as it exhibited the sinuosity index between

1.58, 2.09, 2.73 and 1.90 in 2022. Sub-reach (SRH)

6-10 with a sinuosity index of 2.09 and SRH 9-12

with a sinuosity index of 2.73 are highly vulnerable

sites to flood. The study recommends frequent

monitoring of the deposition of transported materials

particularly along the river curvatures in order to

International Journal of Environmental Engineering and Development

DOI: 10.37394/232033.2024.2.19

Babatope Sunday Olisa,

Mobolaji Stephen Stephens, Ikpechukwu.

Njoku, Chiamaka Lovelyn Olisa

E-ISSN: 2945-1159

220

Volume 2, 2024

ensure manoeuvring lanes that are safe and efficient

for vessel navigation. It is believed that identifying

recurrent changes in the morphology of waterways

(riverways) is essential for inland waterway planning

and the production of nautical charts for safe and

efficient inland transport. The study gives an insight

into further studies towards assessing channel

resilience to floods, straight channel bankline

migrations, determination of sediments transported

and discharge at different locations per period of

time, a medium for predicting the extent of erosion

and curvatures overtime, as well as assessing

uncertainties in the thalweg lines of the waterway

channel using Remote sensing and high tech-

bathymetric techniques.

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Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

Babatope Sunday Olisa carried out field and

collaborate with Stephens and Njoku to develop the

procedures used in carrying out the field study. He

did all typesetting and formatting of the document.

Mobolaji Stephen, Stephens is the major supervisor

of the study. He monitored and carried field records,

statistics and computations of sinuosity indices as

well as plotting charts.

Ikpechukwu. Njoku is the co-supervisor who

coordinated the field study and operated on the

instrument used.

Chiamaka Lovelyn Olisa carried out geospatial

analysis using ArcGIS and Computer aided

techniques.

In summary, everyone contributed in the present

research, at all stages from the formulation of the

problem to the final findings and solution.

Sources of Funding for Research Presented in a

Scientific Article or Scientific Article Itself

No funding was received for conducting this study.

Conflict of Interest

The authors have no conflicts of interest to declare

that are relevant to the content of this article.

International Journal of Environmental Engineering and Development

DOI: 10.37394/232033.2024.2.19

Babatope Sunday Olisa,

Mobolaji Stephen Stephens, Ikpechukwu.

Njoku, Chiamaka Lovelyn Olisa

E-ISSN: 2945-1159

222

Volume 2, 2024